We are continuing our study of the biosynthesis, intracellular processing, packaging and secretion of parathormone and the newly discovered and partially characterized secretory protein of the parthyroid gland. Work during the present year will focus upon the chemical differences between newly synthesized and stored hormone that reflects itself in the ability to mobilize parathormone independently from one or the other of these pools. In addition, we are attempting to correlate the kinetics of biosynthesis and secretion of the parathryroid secretory protein with that of the hormone to identify a physiological role for the former. We also are characterizing cleavage enzymes of the parathyroid including the particulate associated proparathormone: parathormone "convertase" and cathepsin B activity which we have recently isolated from the porcine gland. Other studies will involve structure/function studies of parathormone and proparathormone in terms of the three-dimensional structure required for biological activity.